1. Field of the Invention
The present invention relates to a method of producing a head core slider for a rigid magnetic disk drive, and more particularly to a method of producing such a head core slider, which makes it possible to form a track with a sufficiently small and accurately controlled width, and which consists of a significantly reduced number of process steps.
2. Discussion of the Prior Art
In the art of a rigid magnetic disk drive (sometimes abbreviated as "RDD"), there is known a floating-type magnetic head which employs a bulk type core slider, such as a monolithic type slider as shown generally at 1 in FIG. 1. This core slider 1 is an integral structure consisting of a slider body 2, and a yoke portion 3 which is generally C-shaped in cross section. On one surface of the slider body 2 on which a recording medium in the form of a magnetic disk slidably rotates, there are formed a pair of parallel spaced-apart air bearing portions 4a, 4b which extend in the rotating or sliding direction of the magnetic disk. The sliding surfaces of the air bearing portions 4a, 4b have a suitable height as measured from a recessed portion therebetween. The core slider 1 has a center rail 5 which is formed between the air bearing portions 4a, 4b, so as to extend parallel to the air bearing portions. The center rail 5 serves as an elongate track portion whose surface has the same height as the air bearing portions 4a, 4b. In operation, a selected recording track of the magnetic disk is aligned with the track portion or center rail 5. The yoke portion 3 indicated above is formed integrally with the slider body 2, at one of opposite ends of the center rail 5. The yoke portion 3 and the slider body 2 cooperate with each other to define a closed magnetic path for the magnetic head.
The monolithic type core slider 1 formed solely of a ferrite material is comparatively economical to manufacture. The width of the elongate track portion is determined by tapering or chamfering the parallel edges of the center rail 5. This manner of forming the track portion suffers from difficulties in precisely establishing the desired track width, and in reducing the track width. For meeting the recently growing need of increased density of information per unit area of a recording medium, the required width of the track is less than 20 .mu.m with a permissible error being held to within .+-.2 .mu.m. Further, when the core slider 1 is moved off the surface of the magnetic disk, both of the air bearing portions 4a, 4b should lie within the range of radius of the magnetic disk. Namely, the center rail or track portion 5 located between the two air bearing portions 4a, 4b should be positioned a given distance away from the outer periphery of the magnetic disk in the radially inward direction. Therefore, the effective recording surface area of the magnetic disk is reduced to an extent corresponding to the distance between the track portion 5 and the air bearing portion 4a. 4b. In other words, the data storage capacity of the magnetic disk is limited by the construction of the core slider 1.
There is also known a composite type core slider consisting of a slider body and a head core which are separately prepared. More specifically, a ferrite core having a track portion formed perpendicularly to its surface is partially embedded in and fixed to a non-magnetic slider body. This composite type core slider is advantageous over the monolithic type, in that the track portion can be formed with its width accurately controlled to a desired value, and that the width can be made relatively small. The composite type is further advantageous in that the track portion can be formed in alignment with an air bearing portion, i.e., formed on a line of extension of the air bearing portion, whereby the outer peripheral portion of the magnetic disk can be used as an effective recording area. However, the composite type core slider is disadvantageous in the cost of manufacture, because of the steps of separately preparing the slider body and the core, and then joining these two members together.
A further type of core slider is proposed according to laid-open Publication No. 62-18615 of unexamined Japanese patent application, in an attempt to lower the cost of manufacture while enjoying the functional advantages of the composite type discussed above. In this proposed core slider, a yoke portion is formed integrally with a slider body, at one end of an air bearing portion formed on the slider body, such that the yoke portion and the slider body cooperate to constitute a head core which has a magnetic gap. To produce this core slider, grooves defining a track portion are formed in appropriate two blocks, and the two blocks with the grooves filled with a glass material are butted together and bonded by the glass material, such that selected parts of the joining surfaces define the magnetic gap therebetween. Subsequently, the obtained body of the bonded blocks is subjected to a grooving operation to form the air bearing portion and the yoke portion.
As compared with the monolithic type core slider, the structure proposed in the above-identified publication is easier to manufacture, because the track portion is aligned with the extension line of the air bearing portion, so that both the track portion and the air bearing portion can be formed simultaneously by a grooving operation. Where only one of the two ferrite blocks is subjected to a grooving operation to form the track, the positioning of the two ferrite blocks for alignment of the track grooves is unnecessary. In this case, however, the fringing effect at the edge of the magnetic gap is too large to permit an effective high-density recording operation on the storage medium. Where both of the ferrite blocks are grooved to form the track, it is necessary to establish cumbersome and difficult alignment of the grooves of the two blocks. Furthermore, the cross sectional area of the yoke portion tends to be large, as compared with the aforementioned composite type or monolithic type core slider. In this case, therefore, the inductance of the yoke portion is undesirably high, making it difficult to effect a high-frequency recording, i.e., difficult to achieve a high density of information recorded per unit area of the recording medium.
For producing the above-mentioned conventional core sliders, the grooving operation to form the pair of parallel spaced-apart air bearing portions and the center rail or track portion, and the chamfering of the formed air bearing and track portions are conducted by a machining operation using a grinding stone such as a diamond wheel. The grooving and chamfering operations require a total of eight grinding passes for each core slider, and are the most time-consuming steps of the process. Furthermore, the error in the widths of the air bearing portions and track portion (center rail) cannot be kept to within a permissible range of .+-.3 microns, due to unavoidable positioning error of the grinding wheel, and due to inevitable variations in the thickness or height of the blank for the slider body and positioning error of the yoke portion bonded to the slider body blank. Further, the surfaces finished by the diamond wheel inevitably suffers from chipping of one micron or more.